1,041 research outputs found
STUDIES OF THE MECHANISM OF ACTION OF COBAMIDE COENZYMES
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73404/1/j.1749-6632.1964.tb45046.x.pd
Nonlocal mechanism for cluster synchronization in neural circuits
The interplay between the topology of cortical circuits and synchronized
activity modes in distinct cortical areas is a key enigma in neuroscience. We
present a new nonlocal mechanism governing the periodic activity mode: the
greatest common divisor (GCD) of network loops. For a stimulus to one node, the
network splits into GCD-clusters in which cluster neurons are in zero-lag
synchronization. For complex external stimuli, the number of clusters can be
any common divisor. The synchronized mode and the transients to synchronization
pinpoint the type of external stimuli. The findings, supported by an
information mixing argument and simulations of Hodgkin Huxley population
dynamic networks with unidirectional connectivity and synaptic noise, call for
reexamining sources of correlated activity in cortex and shorter information
processing time scales.Comment: 8 pges, 6 figure
Exact solution of a linear molecular motor model driven by two-step fluctuations and subject to protein friction
We investigate by analytical means the stochastic equations of motion of a
linear molecular motor model based on the concept of protein friction. Solving
the coupled Langevin equations originally proposed by Mogilner et al. (A.
Mogilner et al., Phys. Lett. {\bf 237}, 297 (1998)), and averaging over both
the two-step internal conformational fluctuations and the thermal noise, we
present explicit, analytical expressions for the average motion and the
velocity-force relationship. Our results allow for a direct interpretation of
details of this motor model which are not readily accessible from numerical
solutions. In particular, we find that the model is able to predict
physiologically reasonable values for the load-free motor velocity and the
motor mobility.Comment: 12 pages revtex, 6 eps-figure
An enzymic assay for the determination of millimicrogram quantities of B12-coenzyme
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33457/1/0000861.pd
Theory of Interaction of Memory Patterns in Layered Associative Networks
A synfire chain is a network that can generate repeated spike patterns with
millisecond precision. Although synfire chains with only one activity
propagation mode have been intensively analyzed with several neuron models,
those with several stable propagation modes have not been thoroughly
investigated. By using the leaky integrate-and-fire neuron model, we
constructed a layered associative network embedded with memory patterns. We
analyzed the network dynamics with the Fokker-Planck equation. First, we
addressed the stability of one memory pattern as a propagating spike volley. We
showed that memory patterns propagate as pulse packets. Second, we investigated
the activity when we activated two different memory patterns. Simultaneous
activation of two memory patterns with the same strength led the propagating
pattern to a mixed state. In contrast, when the activations had different
strengths, the pulse packet converged to a two-peak state. Finally, we studied
the effect of the preceding pulse packet on the following pulse packet. The
following pulse packet was modified from its original activated memory pattern,
and it converged to a two-peak state, mixed state or non-spike state depending
on the time interval
Sparse and Dense Encoding in Layered Associative Network of Spiking Neurons
A synfire chain is a simple neural network model which can propagate stable
synchronous spikes called a pulse packet and widely researched. However how
synfire chains coexist in one network remains to be elucidated. We have studied
the activity of a layered associative network of Leaky Integrate-and-Fire
neurons in which connection we embed memory patterns by the Hebbian Learning.
We analyzed their activity by the Fokker-Planck method. In our previous report,
when a half of neurons belongs to each memory pattern (memory pattern rate
), the temporal profiles of the network activity is split into
temporally clustered groups called sublattices under certain input conditions.
In this study, we show that when the network is sparsely connected (),
synchronous firings of the memory pattern are promoted. On the contrary, the
densely connected network () inhibit synchronous firings. The sparseness
and denseness also effect the basin of attraction and the storage capacity of
the embedded memory patterns. We show that the sparsely(densely) connected
networks enlarge(shrink) the basion of attraction and increase(decrease) the
storage capacity
Coulomb blockade and quantum tunnelling in the low-conductivity phase of granular metals
We study the effects of Coulomb interaction and inter-grain quantum
tunnelling in an array of metallic grains using the phase-functional approach
for temperatures well below the charging energy of individual
grains yet large compared to the level spacing in the grains. When the
inter-grain tunnelling conductance , the conductivity in
dimensions decreases logarithmically with temperature
(), while for ,
the conductivity shows simple activated behaviour ().
We show, for bare tunnelling conductance , that the parameter
determines the competition between
charging and tunnelling effects. At low enough temperatures in the regime
, a charge is shared among a finite
number of grains, and we find a soft
activation behaviour of the conductivity, , where is the effective
coordination number of a grain.Comment: 11 pages REVTeX, 3 Figures. Appendix added, replaced with published
versio
Dopant-induced crossover from 1D to 3D charge transport in conjugated polymers
The interplay between inter- and intra-chain charge transport in bulk
polythiophene in the hopping regime has been clarified by studying the
conductivity as a function of frequency (up to 3 THz), temperature and doping
level. We present a model which quantitatively explains the observed crossover
from quasi-one-dimensional transport to three-dimensional hopping conduction
with increasing doping level. At high frequencies the conductivity is dominated
by charge transport on one-dimensional conducting chains.Comment: 4 pages, 2 figure
Teaching strategies and gender in higher education instrumental studios
This study investigates instrumental music teaching strategies in higher education settings, in order to identify those employed and their frequency and context of use. An instrument- and gender-balanced sample of 24 lessons from five institutions was analysed using a researcher-designed observational instrument. The results reveal the predominance of teacher demonstration, general directives and praise as most frequent teaching strategies employed in lessons. Gender differences emerged in the teaching approaches: the male teachers gave more general directives and explanations and the female teachers offered more answers and practice discussions; the male students received the most specific teacher criticism despite uniform use of praise. The findings provide new evidence of teaching practices in advanced instrumental studios and raise questions regarding gender issues in music teaching
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